SIP/ISDN disconnect problem

Our customer has a geographically spread voip. Central site and spokes. Some spokes have local phone ports only and are connected via h.323 peers, some have local pbx connected via sip and gateways there only do number manipulation in sip-to-sip calls.

The lineup is like this: Panasonic TDA200 through E1 Pri (net5 type) to Cisco3825 to Cisco2811 through SIP to Panasonic PBX with SIP card. The problem is that when remote user on sip-emabled panasonic is busy, local user calling him on tda200 trough E1 to 3825 and then through vpn tunnel to 2811 waits for ~30 secs and then gets reorder instead of getting immediate busy tone. When the user is not busy the communication establishes but I have no info about delays.

I have enabled gateway accounting and debugged isdn q931. Dialing panasonic sends 3 digits enblock and then adds 1 in overlap, it cannot do otherwise. That's ok. What I cannot understand is that gw accounting reasonably shows that the call started and ended at the same time and code was user busy. But the gw sends to originating ISDN channel DISCONNECT message only some 30 secs later with normal call clearing code.

To our knowledge this only happens with sip-connected voip spokes, in h.323 there is no such thing.

that is not easily possible. one router is many miles away and have slow and jerky internet connectivity. and I don't see good reason for that: these images are quite good and stable. do you still think that it is not a configuration issue but a software bug?

Anyway, no sip-ua is used. We use sip dial-peers without sip-server. Just peers. On sip-enabled panasonic in remote location with some help from the manufacturer the need to register on server was removed and so it also works in peer-to-peer configuration.